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Groups > linux.kernel > #1379955
| From | "Eric W. Biederman" <ebiederm@xmission.com> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | [PATCH 14/16] vfs: Implement mount_super_once |
| Date | 2016-04-15 18:00 +0200 |
| Message-ID | <roek3-5nF-29@gated-at.bofh.it> (permalink) |
| References | <roeal-5jh-5@gated-at.bofh.it> <roeal-5jh-7@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
The devpts filesystem has a notion of a system or primary instance of
devpts. To retain the notion of a primary system instance of devpts
the code needs a way to allow userspace to mount the internally
mounted instance of devpts when it is not currently mounted by
userspace. The new helper mount_super_once allows that.
The function mount_super_once ignores vfsmounts that are in use but
are not mounted in userspace. The set of ignored mounts includes
internal mounts, lazily unmounted instances of mounts, and
loopback/bind mounts show root directory is not a filesystems root
directory.
Furthermore mount_super_once only allows exporting a mount to
userspace if it can account for every reference in s_active
on the superblock. Ensuring races do not allow two simultaneous
mount requestions export the same filesystem to userspace.
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
---
fs/super.c | 34 ++++++++++++++++++++++++++++++++++
include/linux/fs.h | 2 ++
2 files changed, 36 insertions(+)
diff --git a/fs/super.c b/fs/super.c
index 74914b1bae70..4a6552395fad 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -33,6 +33,7 @@
#include <linux/cleancache.h>
#include <linux/fsnotify.h>
#include <linux/lockdep.h>
+#include "mount.h"
#include "internal.h"
@@ -1101,6 +1102,39 @@ struct dentry *mount_single(struct file_system_type *fs_type,
}
EXPORT_SYMBOL(mount_single);
+struct dentry *mount_super_once(struct super_block *sb, int flags, void *data)
+{
+ /* Allow mounting the specified superblock by userspace if there
+ * are not any existing userspace mounts of it.
+ */
+ struct mount *mnt;
+ int count = 0;
+
+ /* Walk through the existing mounts of this superblock. Fail
+ * if any of those mounts are exported to userspace. Otherwise
+ * increment s_active if the superblock s_active count matches
+ * the number of mounts in the list. This ensures that multiple
+ * simultaneous calls to mount_super_once do not race and result
+ * in the filesystem exported to userspace multiple times.
+ */
+ lock_mount_hash();
+ list_for_each_entry(mnt, &sb->s_mounts, mnt_instance) {
+ if (is_mounted(&mnt->mnt) && (mnt->mnt.mnt_root == sb->s_root)) {
+ unlock_mount_hash();
+ return ERR_PTR(-EBUSY);
+ }
+ count++;
+ }
+ if (atomic_cmpxchg(&sb->s_active, count, count + 1) != count) {
+ unlock_mount_hash();
+ return ERR_PTR(-EBUSY);
+ }
+ unlock_mount_hash();
+ down_write(&sb->s_umount);
+ do_remount_sb(sb, flags, data, 0);
+ return dget(sb->s_root);
+}
+
struct dentry *
mount_fs(struct file_system_type *type, int flags, const char *name, void *data)
{
diff --git a/include/linux/fs.h b/include/linux/fs.h
index aade033bed49..465c1155bf72 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2002,6 +2002,8 @@ extern struct dentry *mount_single(struct file_system_type *fs_type,
extern struct dentry *mount_nodev(struct file_system_type *fs_type,
int flags, void *data,
int (*fill_super)(struct super_block *, void *, int));
+extern struct dentry *mount_super_once(struct super_block *sb,
+ int flags, void *data);
extern struct dentry *mount_subtree(struct vfsmount *mnt, const char *path);
void generic_shutdown_super(struct super_block *sb);
void kill_block_super(struct super_block *sb);
--
2.8.1
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[PATCH 00/13] devpts: New instances for every mount ebiederm@xmission.com (Eric W. Biederman) - 2016-04-05 02:20 +0200
[PATCH 04/13] devpts: Stop rolling devpts_remount by hand in devpts_mount "Eric W. Biederman" <ebiederm@xmission.com> - 2016-04-05 03:50 +0200
[PATCH 05/13] devpts: Fail early (if appropriate) on overmount "Eric W. Biederman" <ebiederm@xmission.com> - 2016-04-05 03:50 +0200
[PATCH 08/13] devpts: Make devpts_kill_sb safe if fsi is NULL "Eric W. Biederman" <ebiederm@xmission.com> - 2016-04-05 03:50 +0200
[PATCH 03/13] devpts: Cleanup newinstance parsing "Eric W. Biederman" <ebiederm@xmission.com> - 2016-04-05 03:50 +0200
[PATCH 06/13] devpts: Use the same default mode for both /dev/ptmx and dev/pts/ptmx "Eric W. Biederman" <ebiederm@xmission.com> - 2016-04-05 03:50 +0200
[PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup "Eric W. Biederman" <ebiederm@xmission.com> - 2016-04-05 03:50 +0200
[PATCH 09/13] devpts: Move the creation of /dev/pts/ptmx into fill_super "Eric W. Biederman" <ebiederm@xmission.com> - 2016-04-05 03:50 +0200
[PATCH 02/13] devpts: More obvious check for the system devpts in pty allocation "Eric W. Biederman" <ebiederm@xmission.com> - 2016-04-05 03:50 +0200
[PATCH 13/13] devpts: Kill the DEVPTS_MULTIPLE_INSTANCE config option "Eric W. Biederman" <ebiederm@xmission.com> - 2016-04-05 03:50 +0200
[PATCH 07/13] devpts: Move parse_mount_options into fill_super "Eric W. Biederman" <ebiederm@xmission.com> - 2016-04-05 03:50 +0200
[PATCH 12/13] devpts: Always return a distinct instance when mounting "Eric W. Biederman" <ebiederm@xmission.com> - 2016-04-05 04:00 +0200
[PATCH 11/13] vfs: Implement mount_super_once "Eric W. Biederman" <ebiederm@xmission.com> - 2016-04-05 04:00 +0200
[PATCH 10/13] devpts: Simplify devpts_mount by using mount_nodev "Eric W. Biederman" <ebiederm@xmission.com> - 2016-04-05 04:00 +0200
Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup Al Viro <viro@ZenIV.linux.org.uk> - 2016-04-05 05:00 +0200
Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup Al Viro <viro@ZenIV.linux.org.uk> - 2016-04-05 05:10 +0200
Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup ebiederm@xmission.com (Eric W. Biederman) - 2016-04-08 21:10 +0200
Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup Linus Torvalds <torvalds@linux-foundation.org> - 2016-04-07 18:10 +0200
Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup ebiederm@xmission.com (Eric W. Biederman) - 2016-04-08 21:10 +0200
Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup Linus Torvalds <torvalds@linux-foundation.org> - 2016-04-08 21:10 +0200
Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup ebiederm@xmission.com (Eric W. Biederman) - 2016-04-08 22:20 +0200
Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup Andy Lutomirski <luto@amacapital.net> - 2016-04-08 22:50 +0200
Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup ebiederm@xmission.com (Eric W. Biederman) - 2016-04-08 23:50 +0200
Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup Andy Lutomirski <luto@amacapital.net> - 2016-04-09 00:00 +0200
Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup Linus Torvalds <torvalds@linux-foundation.org> - 2016-04-09 00:00 +0200
Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup ebiederm@xmission.com (Eric W. Biederman) - 2016-04-09 01:20 +0200
Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk> - 2016-04-09 15:20 +0200
Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup "H. Peter Anvin" <hpa@zytor.com> - 2016-04-09 16:20 +0200
Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup ebiederm@xmission.com (Eric W. Biederman) - 2016-04-09 17:00 +0200
Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup "H. Peter Anvin" <hpa@zytor.com> - 2016-04-10 00:50 +0200
Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup Linus Torvalds <torvalds@linux-foundation.org> - 2016-04-10 02:10 +0200
Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup "H. Peter Anvin" <hpa@zytor.com> - 2016-04-10 02:20 +0200
Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup Linus Torvalds <torvalds@linux-foundation.org> - 2016-04-10 02:20 +0200
Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup Andy Lutomirski <luto@amacapital.net> - 2016-04-10 02:50 +0200
Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup "H. Peter Anvin" <hpa@zytor.com> - 2016-04-11 17:10 +0200
Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup Al Viro <viro@ZenIV.linux.org.uk> - 2016-04-12 03:40 +0200
Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup Andy Lutomirski <luto@amacapital.net> - 2016-04-11 22:20 +0200
Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup "H. Peter Anvin" <hpa@zytor.com> - 2016-04-11 22:30 +0200
Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup ebiederm@xmission.com (Eric W. Biederman) - 2016-04-12 01:50 +0200
Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup Linus Torvalds <torvalds@linux-foundation.org> - 2016-04-12 02:10 +0200
Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup ebiederm@xmission.com (Eric W. Biederman) - 2016-04-12 02:30 +0200
Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup Linus Torvalds <torvalds@linux-foundation.org> - 2016-04-12 03:20 +0200
Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup "H. Peter Anvin" <hpa@zytor.com> - 2016-04-12 03:20 +0200
Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup ebiederm@xmission.com (Eric W. Biederman) - 2016-04-12 03:40 +0200
Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup Al Viro <viro@ZenIV.linux.org.uk> - 2016-04-12 03:50 +0200
Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup Al Viro <viro@ZenIV.linux.org.uk> - 2016-04-12 03:40 +0200
Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup ebiederm@xmission.com (Eric W. Biederman) - 2016-04-12 04:30 +0200
Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup ebiederm@xmission.com (Eric W. Biederman) - 2016-04-11 22:30 +0200
Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup Andy Lutomirski <luto@amacapital.net> - 2016-04-12 19:50 +0200
Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup Linus Torvalds <torvalds@linux-foundation.org> - 2016-04-12 20:20 +0200
Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup "H. Peter Anvin" <hpa@zytor.com> - 2016-04-12 21:20 +0200
[PATCH 01/16] devpts: Attempting to get it right ebiederm@xmission.com (Eric W. Biederman) - 2016-04-15 17:50 +0200
[PATCH 08/16] devpts: Stop rolling devpts_remount by hand in devpts_mount "Eric W. Biederman" <ebiederm@xmission.com> - 2016-04-15 17:50 +0200
[PATCH 05/16] vfs: Allow unlink, and rename on expirable file mounts "Eric W. Biederman" <ebiederm@xmission.com> - 2016-04-15 17:50 +0200
[PATCH 04/16] devpts: Teach /dev/ptmx to automount the appropriate devpts via path lookup "Eric W. Biederman" <ebiederm@xmission.com> - 2016-04-15 17:50 +0200
Re: [PATCH 04/16] devpts: Teach /dev/ptmx to automount the appropriate devpts via path lookup Jann Horn <jann@thejh.net> - 2016-04-16 00:10 +0200
Re: [PATCH 04/16] devpts: Teach /dev/ptmx to automount the appropriate devpts via path lookup ebiederm@xmission.com (Eric W. Biederman) - 2016-04-19 21:00 +0200
[PATCH 09/16] devpts: Fail early (if appropriate) on overmount "Eric W. Biederman" <ebiederm@xmission.com> - 2016-04-15 17:50 +0200
[PATCH 10/16] devpts: Move parse_mount_options into fill_super "Eric W. Biederman" <ebiederm@xmission.com> - 2016-04-15 17:50 +0200
[PATCH 06/16] devpts: More obvious check for the system devpts in pty allocation "Eric W. Biederman" <ebiederm@xmission.com> - 2016-04-15 17:50 +0200
[PATCH 01/16] devpts: Use the same default mode for both /dev/ptmx and dev/pts/ptmx "Eric W. Biederman" <ebiederm@xmission.com> - 2016-04-15 17:50 +0200
[PATCH 12/16] devpts: Move the creation of /dev/pts/ptmx into fill_super "Eric W. Biederman" <ebiederm@xmission.com> - 2016-04-15 18:00 +0200
[PATCH 11/16] devpts: Make devpts_kill_sb safe if fsi is NULL "Eric W. Biederman" <ebiederm@xmission.com> - 2016-04-15 18:00 +0200
[PATCH 16/16] devpts: Kill the DEVPTS_MULTIPLE_INSTANCE config option "Eric W. Biederman" <ebiederm@xmission.com> - 2016-04-15 18:00 +0200
[PATCH 15/16] devpts: Always return a distinct instance when mounting "Eric W. Biederman" <ebiederm@xmission.com> - 2016-04-15 18:00 +0200
[PATCH 13/16] devpts: Simplify devpts_mount by using mount_nodev "Eric W. Biederman" <ebiederm@xmission.com> - 2016-04-15 18:00 +0200
[PATCH 14/16] vfs: Implement mount_super_once "Eric W. Biederman" <ebiederm@xmission.com> - 2016-04-15 18:00 +0200
Re: [PATCH 14/16] vfs: Implement mount_super_once Linus Torvalds <torvalds@linux-foundation.org> - 2016-04-16 01:10 +0200
Re: [PATCH 14/16] vfs: Implement mount_super_once ebiederm@xmission.com (Eric W. Biederman) - 2016-04-19 20:40 +0200
Re: [PATCH 14/16] vfs: Implement mount_super_once "H. Peter Anvin" <hpa@zytor.com> - 2016-04-19 21:00 +0200
Re: [PATCH 14/16] vfs: Implement mount_super_once ebiederm@xmission.com (Eric W. Biederman) - 2016-04-19 21:20 +0200
Re: [PATCH 14/16] vfs: Implement mount_super_once "H. Peter Anvin" <hpa@zytor.com> - 2016-04-19 21:30 +0200
Re: [PATCH 14/16] vfs: Implement mount_super_once ebiederm@xmission.com (Eric W. Biederman) - 2016-04-20 05:40 +0200
Re: [PATCH 14/16] vfs: Implement mount_super_once "Austin S. Hemmelgarn" <ahferroin7@gmail.com> - 2016-04-20 14:00 +0200
Re: [PATCH 14/16] vfs: Implement mount_super_once "H. Peter Anvin" <hpa@zytor.com> - 2016-04-20 18:20 +0200
Re: [PATCH 14/16] vfs: Implement mount_super_once "H. Peter Anvin" <hpa@zytor.com> - 2016-04-19 21:30 +0200
Re: [PATCH 14/16] vfs: Implement mount_super_once "H. Peter Anvin" <hpa@zytor.com> - 2016-04-19 21:00 +0200
Re: [PATCH 14/16] vfs: Implement mount_super_once Linus Torvalds <torvalds@linux-foundation.org> - 2016-04-20 01:30 +0200
Re: [PATCH 14/16] vfs: Implement mount_super_once Linus Torvalds <torvalds@linux-foundation.org> - 2016-04-20 03:30 +0200
Re: [PATCH 14/16] vfs: Implement mount_super_once "H. Peter Anvin" <hpa@zytor.com> - 2016-04-20 03:50 +0200
Re: [PATCH 01/16] devpts: Attempting to get it right Andy Lutomirski <luto@amacapital.net> - 2016-04-15 18:50 +0200
Re: [PATCH 01/16] devpts: Attempting to get it right ebiederm@xmission.com (Eric W. Biederman) - 2016-04-15 23:00 +0200
Re: [PATCH 01/16] devpts: Attempting to get it right "H. Peter Anvin" <hpa@zytor.com> - 2016-04-15 23:40 +0200
Re: [PATCH 01/16] devpts: Attempting to get it right ebiederm@xmission.com (Eric W. Biederman) - 2016-04-19 21:20 +0200
Re: [PATCH 01/16] devpts: Attempting to get it right Linus Torvalds <torvalds@linux-foundation.org> - 2016-04-16 20:40 +0200
Does anyone care about a race free ptsname? ebiederm@xmission.com (Eric W. Biederman) - 2016-04-19 21:00 +0200
Re: Does anyone care about a race free ptsname? "H. Peter Anvin" <hpa@zytor.com> - 2016-04-19 21:30 +0200
Re: Does anyone care about a race free ptsname? ebiederm@xmission.com (Eric W. Biederman) - 2016-04-19 22:50 +0200
Re: Does anyone care about a race free ptsname? "H. Peter Anvin" <hpa@zytor.com> - 2016-04-19 23:10 +0200
Re: Does anyone care about a race free ptsname? "Serge E. Hallyn" <serge@hallyn.com> - 2016-04-19 22:50 +0200
Re: Does anyone care about a race free ptsname? Linus Torvalds <torvalds@linux-foundation.org> - 2016-04-20 01:30 +0200
Re: Does anyone care about a race free ptsname? "H. Peter Anvin" <hpa@zytor.com> - 2016-04-20 01:50 +0200
Re: Does anyone care about a race free ptsname? Linus Torvalds <torvalds@linux-foundation.org> - 2016-04-20 02:20 +0200
Re: Does anyone care about a race free ptsname? "Serge E. Hallyn" <serge@hallyn.com> - 2016-04-20 03:50 +0200
Re: [PATCH 01/16] devpts: Attempting to get it right ebiederm@xmission.com (Eric W. Biederman) - 2016-04-20 00:20 +0200
Re: [PATCH 01/16] devpts: Attempting to get it right Linus Torvalds <torvalds@linux-foundation.org> - 2016-04-20 01:40 +0200
Re: [PATCH 01/16] devpts: Attempting to get it right Peter Hurley <peter@hurleysoftware.com> - 2016-04-20 02:30 +0200
Re: [PATCH 01/16] devpts: Attempting to get it right Peter Hurley <peter@hurleysoftware.com> - 2016-04-20 02:50 +0200
[PATCH] devpts: Make each mount of devpts an independent filesystem. ebiederm@xmission.com (Eric W. Biederman) - 2016-04-20 05:20 +0200
Re: [PATCH] devpts: Make each mount of devpts an independent filesystem. Al Viro <viro@ZenIV.linux.org.uk> - 2016-04-20 05:30 +0200
Re: [PATCH] devpts: Make each mount of devpts an independent filesystem. ebiederm@xmission.com (Eric W. Biederman) - 2016-04-20 06:00 +0200
Re: [PATCH] devpts: Make each mount of devpts an independent filesystem. Al Viro <viro@ZenIV.linux.org.uk> - 2016-04-20 06:20 +0200
Re: [PATCH] devpts: Make each mount of devpts an independent filesystem. ebiederm@xmission.com (Eric W. Biederman) - 2016-04-20 06:40 +0200
Re: [PATCH] devpts: Make each mount of devpts an independent filesystem. Konstantin Khlebnikov <koct9i@gmail.com> - 2016-04-20 06:40 +0200
Re: [PATCH] devpts: Make each mount of devpts an independent filesystem. Linus Torvalds <torvalds@linux-foundation.org> - 2016-04-20 07:00 +0200
Re: [PATCH] devpts: Make each mount of devpts an independent filesystem. ebiederm@xmission.com (Eric W. Biederman) - 2016-04-20 17:10 +0200
Re: [PATCH] devpts: Make each mount of devpts an independent filesystem. Konstantin Khlebnikov <koct9i@gmail.com> - 2016-04-20 17:40 +0200
Re: [PATCH] devpts: Make each mount of devpts an independent filesystem. ebiederm@xmission.com (Eric W. Biederman) - 2016-04-20 18:10 +0200
[PATCH v2] devpts: Make each mount of devpts an independent filesystem. ebiederm@xmission.com (Eric W. Biederman) - 2016-04-20 19:20 +0200
Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup ebiederm@xmission.com (Eric W. Biederman) - 2016-04-12 02:10 +0200
Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup Linus Torvalds <torvalds@linux-foundation.org> - 2016-04-12 02:10 +0200
Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup ebiederm@xmission.com (Eric W. Biederman) - 2016-04-12 02:40 +0200
Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup Linus Torvalds <torvalds@linux-foundation.org> - 2016-04-12 03:00 +0200
Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup ebiederm@xmission.com (Eric W. Biederman) - 2016-04-11 22:20 +0200
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